This application relates to dispensing.
Many applications call for an automatic mechanism that dispenses a desired amount of a material. For example, in an automatic assembly line used in producing semiconductor-based electronic circuits, when an electronic part such as a chip resistor, a capacitor, or a packaged integrated circuit ("IC") is to be mounted onto a substrate having a circuit pattern formed thereon, creamy solder is deposited in a selected position on the substrate by use of a dispenser and then the electronic part is automatically mounted in the selected position by use of a chip mounter.
The dispenser typically includes a tube needle fixed at a bottom end of the dispenser, a syringe that stores the creamy solder above the tube needle, and a plunger housed within the syringe above the creamy solder in an upwardly and downwardly movable manner for discharging the creamy solder by a downward displacement of the plunger towards the tube needle. The downward displacement of the plunger pushes the creamy solder down within the syringe and discharges the creamy solder from a bottom end of the tube needle.
Typically, the plunger is driven down towards the tube needle by air under pressure. However, air under pressure compresses readily and can escape around the plunger into a space below the plunger. As a result, as air is added under pressure, the plunger may not reliably move downward as desired and creamy solder may not be dispensed in a desired amount.
A desired amount of material may be dispensed by a device that employs an auger or screw that is rotated to cause dispensing. In the device, the rotative force is converted to linear, outward force that drives the material being dispensed.